1. Field of the Invention
This invention relates to electric rotating machines, and more particularly relates to self-starting unidirectional synchronous and stepper motors.
2. Brief Description of the Prior Art
There has been developed a class of electric motors which are compact and extremely efficient. Representative motors of this type are disclosed for example in U.S. Pat. No. 3,370,189, to Arthur W. Haydon, U.S. Pat. No. 3,495,107, to Arthur W. Haydon, U.S. Pat. No. 3,564,314, to Arthur W. Haydon, U.S. Pat. No. 3,671,841 to Gotfred O. Hoffman, U.S. Pat. No. 3,495,113, to Arthur W. Haydon, U.S. Pat. No. 3,626,263, to Maurice G. McBride, and U.S. Pat. No. 4,004,168, to Arthur W. Haydon. To achieve unidirectional self-starting characteristics, motors of this type include auxiliary devices, such as shading coils or auxiliary pole pieces, so that upon energization of the stator field coil, the rotor will uniformly and consistantly begin its rotation in a predetermined direction.
Electric motors of the foregoing type are frequently used in situations where the device must operate reliably for extended periods of time in a sealed or inaccessible location. For example, motors of this type are often used in airborne or space vehicles. Under such conditions, the motors should be as simply constructed as possible, with a minimum number of parts, because the potential for failure is directly related to the number of such parts. In addition, in aerospace applications, the weight of the motor whould advantageously be as small as possible.
To further improve the overall compactness and efficiency of the motors, and, at the same time, to reduce their cost to the ultimate consumer, it is desirable to simplify the design of the stator as much as possible. For example, the design of the field coil itself should be made as simple as possible, for example, as a helical winding surrounding the rotor. In addition, it would be advantageous to eliminate such parts as shading rings or auxiliary pole pieces. However, attempts to eliminate such parts, or to provide non-exotic stator windings, have in the past often resulted in motors that either are not self-starting, or do not consistently turn in the proper direction.
Difficulties have also been encountered in the assembly of previously-proposed motors, particularly in the successive steps necessary to assemble all of the pole-pieces and auxiliary parts of the stator. These numerous steps have resulted in a high labor cost in constructing the motors.